fix(qemu): fix variable may be used uninitialized error

When building with LTO, the compiler discovers that it is possible to
use the `ns_buf_base` variable without writing to it. This happens on
error by dt_add_ns_buf_node(). Check its return value and panic() if
something went wrong so the error doesn't propagate silently.

Change-Id: Ia6aa83b0b9301b2db7bfa6ecd66396c37a57e816
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
diff --git a/plat/qemu/common/qemu_spm.c b/plat/qemu/common/qemu_spm.c
index abedbe4..873b97b 100644
--- a/plat/qemu/common/qemu_spm.c
+++ b/plat/qemu/common/qemu_spm.c
@@ -129,7 +129,9 @@
 {
 	uintptr_t ns_buf_base;
 
-	dt_add_ns_buf_node(&ns_buf_base);
+	if (dt_add_ns_buf_node(&ns_buf_base) != 0) {
+		panic();
+	}
 
 	plat_qemu_secure_partition_mmap[0].base_pa = ns_buf_base;
 	plat_qemu_secure_partition_mmap[0].base_va = ns_buf_base;